Myxococcus xanthus is a gram negative soil organism that displays two modes of motility; adventurous (A-motility) and social (S-motility), which act synergistically to coordinate the migration across surfaces during vegetative growth, forming surface swarms. Under stress the bacteria aggregate and form fruiting bodies where sporulation takes place. M. xanthus has become a model organism for studying self-organised collective behaviours of bacteria.
We have developed a novel interstitial biofilm assay that promotes rapid, active expansion of M. xanthus communities. The resultant biofilms are characterised by the development of a complex network that appears more extensive and intricate than has been previously described for M. xanthus swarms. Furthermore, we identified that a series of phase-bright trails were present on the underlying media that correlated directly to the original biofilm morphology and were reminiscent of the phase-bright trails characteristic of M. xanthus surface swarms. By imaging the topography of the underlying media we found that these phase-bright trails were furrows within the media. We have also determined that these furrows contain a bed of extracellular matrix material comprised of exopolysaccharides, eDNA and lipids.
Our observations have shown that interstitial biofilms of M. xanthus are characterised by dramatic self-organised large-scale patterning that arises through complex co-ordinated cell movements. We have previously described the importance of stigmergy; a concept of self-organisation utilising persistent cues within the environment, during Pseudomonas aeruginosa active biofilm expansion. Our findings indicate that M. xanthus also employs similar methods of stigmergic self-organisation during active biofilm expansion.